Re-add syntax highlighting to daily emails and

...ATDC lessons

source/_daily_emails/2023-08-20.md

@@ -12,7 +12,7 @@ Following yesterday's email about input validation, guard clauses and assertion
 
 For example:
 
-```php
+```language-php
 function createJourney(string $from, string $to, int $duration): void {
   var_dump($from, $to, $duration);
 }
@@ -22,13 +22,13 @@ In this code, each parameter has a type, but there's no validation on the values
 
 If I run this:
 
-```plain
+```language-plain
 createJourney('', '', -10);
 ```
 
 I would get this output:
 
-```plain
+```language-plain
 string(0) ""
 string(0) ""
 int(-10)
@@ -44,7 +44,7 @@ I can use an assertion library or throw my own Exceptions if the values pass the
 
 For example:
 
-```php
+```language-php
 function createJourney(string $from, string $to, int $duration): void {
   Assert::stringNotEmpty($from);
   Assert::stringNotEmpty($to);